1. Field of the Invention
The present invention relates to a mold clamping apparatus of an injection molding machine, equipped with a drive mechanism for opening/closing and clamping a mold by use of a drive motor and a ball-screw mechanism.
2. Description of the Related Art
A conventional mold clamping apparatus of an injection molding machine, equipped with a drive mechanism for opening/closing and clamping a mold by use of a drive motor and a ball-screw mechanism, is disclosed in, for example, Japanese Utility Model Publication (kokoku) No. 8(1996)-1847.
The disclosed mold clamping apparatus includes a first ball nut disposed rotatably on a movable platen; a mold-clamping motor for rotating the first ball nut; a second ball screw rotatably screw-engaged with the movable platen provided on a base; a mold-opening/closing motor for rotating the second ball screw; a first ball screw screw-engaged with the first ball nut and having a spline portion; a mold-clamping housing disposed on the base and having a hole portion formed therein in order to receive the spline portion; a support plate disposed in the vicinity of the hole portion and adapted to hold the spline portion; and a clutch plate disposed movably and adapted to stop up the hole portion.
However, the above-mentioned conventional mold clamping apparatus involves the following problems.
First, since a drive system for opening/closing the mold at high speed and a drive system for clamping the mold at high pressure are independent of each other and do not assume symmetry (are not balanced), the drive systems involve difficulty in operating smoothly and place limitations on an increase in speed of opening/closing the mold and an increase in mold clamp pressure.
Second, mechanism components are independent of each other and are dispersed; in other words, configuration or layout is not designed rationally, resulting in an increase in the overall size of the mold clamping apparatus.
An object of the present invention is to provide a mold clamping apparatus of an injection molding machine which can make its drive systems symmetric (balanced) to thereby enable smooth operation and increase operation speed and clamp pressure sufficiently.
Another object of the present invention is to provide a mold clamping apparatus of an injection molding machine, capable of attaining a compact overall size thereof through rational design of configuration and layout.
To achieve the above objects, the present invention provides a mold clamping apparatus of an injection molding machine having a drive mechanism which performs mold opening/closing operation and mold clamping operation by use of a drive motor and a ball-screw mechanism. The drive mechanism comprises: a first drive mechanism portion including a first drive motor portion and a first ball-screw mechanism portion and advancing and retracting a movable platen in order to effect high-speed mold opening/closing operation; a second drive mechanism portion including a second drive motor portion and a second ball-screw mechanism portion and pressing a pressure platen in order to effect high-pressure mold clamping operation; and a clutch mechanism for connecting the pressure platen to the movable platen in a pressure applicable manner when the movable platen is located at a mold close position.
In the mold clamping apparatus, the first drive mechanism portion advances and retracts the movable platen in order to effect high-speed mold opening/closing operation. When the movable platen has reached the mold close position (when the mold has been closed), the clutch mechanism connects the pressure platen to the movable platen. That is, when the movable platen has reached the mold close position, a predetermined gap is provided between a pressure receiving portion of the movable platen and the pressure platen, to thereby enable insertion of paired clutch plates into the gap. After the insertion of paired clutch plates, the second drive mechanism portion advances the pressure platen via a toggle link mechanism in order to apply pressure to the pressure receiving portion via the clutch plates. With this operation, pressure is applied to the movable platen in order to effect high-pressure mold clamping.